Circuits including electronic parts such as transistors, etc., and electric parts such as motors, etc. used for computers and their peripherals, are designed on substrates. These substrates, etc. are housed in resin cases (hereafter called “connector-integrated cases”) wherein connectors are integrally formed. Terminals connected to the substrates, etc. protrude from the connectors to the outside of the boxes so that the terminals can be attached to other parts through the connectors.
FIG. 13 is a perspective view of a conventional connector-integrated case 100.
FIG. 14 is a cross-sectional view of a connector-integrated case 100′ having the same construction as the connector-integrated case 100 except that it has a through hole 500 provided in a lid 300, and is equivalent to a cross-sectional view along the line 14-14 in FIG. 13.
The connector-integrated case 100 comprises a box 200 and a lid 300 made of resin such as plastic, etc. Inside a connector C provided on one side of the box 200, there is a plurality of terminals T protruding from within to the outside of the box 200 (see FIG. 14).
This terminal T is connected, at one end, to a circuit of a substrate B secured in the box 200 and is attachable, at the other end, to another member through the connector C.
After securing a substrate B inside the box 200, a seal packing (not shown) is placed between an end face of the box 200 and the lid 300. Then, the box 200 and the lid 300 are secured with screws, etc (not shown).
The connector-integrated case 100 like this has to be completely watertight so that moisture may not enter inside.
When there is communication between outside air and the inside of the connector-integrated case 100, conditions of the outside air such as outside air temperature and humidity, etc. may influence the substrate B inside the connector-integrated case 100.
In particular, when humid outside air is taken into the connector-integrated case 100, metal parts such as circuits, etc. of the substrate B are corroded by moisture contained in the outside air, often causing electrical contact failures.
Therefore, the connector-integrated case 100 must be highly airtight.
On the other hand, when electric and electronic parts in use inside the connector-integrated case 100 generate heat and the temperature inside the connector-integrated case 100 increases, the inside air may expand to produce high pressure. Further, under certain conditions, the internal pressure may become lower than atmospheric pressure, that is, it may become subatmospheric.
In order to cope with the thus-produced difference in pressure between the interior and exterior of the connector-integrated case 100, it is necessary to provide a through hole in the connector-integrated case 100. However, provision of such a through hole inevitably lowers the waterproof quality and airtightness.
Therefore, in the past, as shown in a cross-sectional view of FIG. 14, a through hole 500 is formed in an upper surface of the lid 300 or in a side face of the box 200. The through hole 500 was covered with woven fabric, etc. preventing moisture and oil content from passing through, and allowing only air to pass, to equalize the internal and external pressures while maintaining a waterproof quality and airtightness.
An example of a woven fabric preventing moisture and oil content from passing through and allowing only air to pass is a porous film 400 made of fluorocarbon resin, etc., which is bonded to the box 200 or to the lid 300 by a double-sided tape or by an adhesive.
Since the porous film 400 covering the through hole 500 is made of fluorocarbon resin and the like, the double-sided tape and adhesive, etc. cannot achieve sufficient adhesion, and, as a result, the porous film 400 sometimes peels in use.
Therefore, in a certain connector-integrated case, the porous film 400 is cut into a circular shape and fitted into a metal ring, which is crimped to hold the porous film 400. Then the porous film 400, fitted in the metal ring, is secured to the required position on the box 200 or the lid 300 by insert molding or further crimping.
The porous film 400 is sometimes bonded at the required position on the box 200 or lid 300 by heat sealing or laser seizing.
However, it requires processing time to crimp a metal ring to the periphery of the porous film 400. Further, excessively strong crimping gives rise to the problem of damage to the porous film 400.
Further, bonding the porous film 400 by heat sealing or laser seizing, requires special equipment, resulting in additional cost. Also, during such procedures, it is difficult to locate the porous film 400 at the proper position with respect to the through hole 500. Further, since it is not possible to exert pressure to the porous film 400, sufficient bonding strength cannot be obtained.